An inflator for inflating an inflatable vehicle occupant protection device, such as an air bag, contains a body of ignitable gas generating material. The inflator further includes an igniter. The igniter is actuated so as to ignite the body of gas generating material when the vehicle experiences a collision for which inflation of the air bag is desired. As the body of gas generating material burns, it generates a volume of inflation gas. The inflation gas is directed into the air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
It is desirable that the gas generating material for inflating an inflatable vehicle occupant protection device meet a number of technical requirements. For instance, the gas generated by combustion of the gas generating material should be substantially free of toxic materials. It should also be essentially smoke-free and should have a low water content. The gas generating material must be chemically and physically stable over a wide temperature range, and should have ignition and combustion characteristics suitable for use in a vehicle occupant protection device.
High energy organic compounds such as 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetracyclooctane (HMX) have been proposed for use in rockets and gun powder. U.S. Pat. No. 3,943,209 discloses a rocket or gunpowder propellant formulation that comprises HMX and ammonium nitrate (AN). The advantage of ammonium nitrate in the formulation is that the gas effluent from combustion of the formulation is smokeless. However, the ammonium nitrate is present in the formulation in a relative large percent. Ammonium nitrate can undergo phase changes with changes in temperature. A vehicle occupant protection device may be exposed to wide temperature changes, and thus any body of gas generating material in a vehicle occupant protection device which comprises a large amount of ammonium nitrate may physically degrade over time. Also, compositions containing large amounts of ammonium nitrate may be difficult to ignite, and/or may not sustain combustion at low ambient temperature.
Perchlorates such as potassium perchlorate (KClO.sub.4) and ammonium perchlorate (NH.sub.4 ClO.sub.4) are good oxidizers. In combination with an organic fuel component, they burn rapidly. However, they can produce hydrogen chloride (HCl), in the form of a mist, or potassium chloride (KCl), in the form of a white smoke. Both products are undesirable, in large quantities, in a combustion gas product for inflating a vehicle occupant protection device.